1. Field of the Invention
The present invention relates to a recyclable biomass-derived epoxy resin composition.
2. Description of Related Art
The need to take international action against global warming has become urgent. Carbon-neutral products and recyclable products are expected from various fields to achieve the society which cuts the amount of carbon dioxide. Thermoplastic polylactic acid or bio-alcohol has been studied as the carbon-neutral product. As part of the study, lignin that is not effectively used yet has attracted attention. The lignin is a principal component of wood, and has a heat resistant structure with a polyphenol skeleton. The lignin content of wood is about 25%. The lignin constitutes an interpenetrating polymer network (IPN) together with cellulose which is contained in about 50% in the wood. The lignin is a complicated cross-linked polymeric compound, and is difficult to be separated off. For this reason, the lignin is defined as an obstacle interfering with production of the cellulose. Most of the lignin is treated as waste. However, the lignin has a heat resistant structure which is very rare among plant biomasses. In order to make effective use of such a structure, various techniques have been studied to extract the lignin in a high yield. Further, a low-molecular lignin has been developed. The application of the lignin as an insulating material by converting the lignin into an epoxy resin has been studied (see, for example, Japanese Patent Application Laid-Open No. 2005-199209 (Patent Document 1)).
In recycle technology, the recovery rate of used paper is 75%, and the recovery rate of metals from four kinds of electric household appliances based on home appliance recycling law is almost 100%. As to resin, however, only a thermoplastic resin is recycled by pelletization according to the home appliance recycle law. The recycle of a thermosetting resin such as an epoxy resin cured material has not been promoted. This is because the thermosetting resin is insoluble and infusible and thus requires much energy for depolymerization, which leads to the imbalance of the energy budget. In recent years, however, a depolymerization method is proposed which involves ester exchange of a thermosetting polymer containing many ester linkages with an alkali metal and an alcohol at normal pressure into a low-molecular weight compound (see, for example, Japanese Patent Application Laid-Open No. 2005-255835 (Patent Document 2)).
An example of recycling of epoxy resin from an acid anhydride-containing epoxy resin cured material is disclosed in Non-Patent Document 1 (Kao Min Tai, Research Committee of the Japan Society of Epoxy Resin Technology, Summary of Special Lecture by Recycle Committee (2000)).